The King of Braves: GaoGaiGar

In the year 2005, a race of alien monsters called Zonders emerge from underground and launch a series of attacks on the city of Tokyo. The only defense against these creatures is the secret agency known as the Gutsy Geoid Guard (or 3G) and their ultimate weapon, the awesome giant robot GaoGaiGar. GaoGaiGar's pilot, Guy Shishio, is a former astronaut who was nearly killed two years before when the Zonders first crashed to earth. Guy's life was spared when a mysterious robot lion called Galeon pulled him from the burning shuttle and brought him to Earth. Guy's father, Leo, then used Galeon's technology to rebuild his shattered son as a cyborg, in the hopes that he could stop the aliens when they appear. Now, with Galeon as its core, GaoGaiGar fights to protect Earth. He is aided by a team of transforming robots and by a young boy named Mamoru, who has the power to purify the Zonders' cores, and seems to be connected to the mysterious Galeon. (Source: Anime News Network)

Gurren Lagann

In a far away future, mankind lives underground in huge caves, unknowing of a world above with a sky and stars. In the small village of Jiha, Simon, a shy boy who works as a digger discovers a strange glowing object during excavation. The enterprising Kamina, a young man with a pair of rakish sunglasses and the passion of a firey sun, befriends Simon and forms a small band of brothers, the Gurren Brigade, to escape the village and break through the ceiling of the cave to reach the surface, which few believe exist. The village elder won't hear of such foolishness and punishes the Brigade. However, when disaster strikes from the world above and the entire village is in jeopardy, it's up to Simon, Kamina, a girl with a big gun named Yoko, and the small yet sturdy robot, Lagann, to save the day. The new friends journey to the world above and find that the surface is a harsh battlefield, and it's up to them to fight back against the rampaging Beastmen to turn the tide in the humans' favor! Pierce the heavens, Gurren Lagann!

Mazinkaiser

In one of their epic battles, the Mazinger Team suffers a crushing defeat at the hands of Dr. Hell and his minions after Mazinger Z is stolen and its pilot, the legendary Kouji Kabuto, is rendered missing in action. Just when Dr. Hell's second-in-command Baron Ashura uses Mazinger Z against our heroes, Kouji makes a surprise return in Mazinkaiser - an all-new Mazinger with heavier armor and deadlier attacks. (Source: Anime News Network)

Energetic Bomb Ganbaruger

Koutarou's father is trying to train his son in the art of the ninja, but a mis-hit bomb accidently damages a shrine and releases a great demon that Eldoran had been keeping contained. Eldoran manages to contain him, but one of his servants manages to escape as well, and now attempts to free his master. To stop him, Eldoran grants the three mecha Gotiger, King Elephan, and Mach Eagle to Koutarou and his two friends, as well as suits that grant each of them a special power. Miracle Ninja Ganbare Team is born! (Source: starfox.net)

Magne Robo Gakeen

Dr. Kazuki, who perceived of an invasion of Earth by the Izaru people builds a robot based on the science of magnetism and sphere joint theory. Undergoing a dangerous augmentation process, Dr. Kazuki's daughter Mai becomes the pilot of "Mighty" or "Magnetman Minus". Takeshi Hojo becomes the pilot of "Puraiza" or "Magnetman Plus". The pilots would hold each other and then physically trasform their joint bodies in a metallic plate locking itself on the Gakeen (Short for "Gathering Keen") robot's frame thus enabling the super robot to move and fight. This sequence was notable, to an adult's eye, for its almost-sexual connotation. (Source: Wikipedia)